In reproducing color or monochrome images, conventional printers are typically able to reproduce an input color or tone as one of a finite number of grey levels. An Flectro-Photography (EP) printer, for example, may be used to represent the available number of grey levels. Some printer systems utilize an error diffusion algorithm to improve a reproduced image quality. However, such systems known in the art suffer from multiple problems, such as those identified in FIGS. 1A-C.
In FIG. 1A a conventional system for reproducing images identifies an input color that may be classified as having a dark tone 2. The system reproduces the dark tone 2 as output color 12. Output color 12 includes a combination of dark tone pixels 5 and light tone pixels 10 that are generated in an attempt to reproduce the dark tone 2. The combination of multiple tone pixels results in an unpleasant patterning that appears irregular or non-uniform in tonal quality. In addition, dot gain 15 appears in regions of pixel groupings, as ink is attracted from neighboring pixels, of either light or dark tone 5, 10.
In FIG. 1B a conventional printer system identifies an input color that may be classified as having a mid-tone 4. The system reproduces the mid-tone 4 as output color 14, including many light tone pixels 10. Light toned pixels 10 are preferentially selected by conventional error diffusion algorithms, such that the mid-tone 4 is reproduced using a relatively large number of light tone pixels 10. As in FIG. 1A, the relatively large number of pixels results in dot gain 15.
In FIG. 1C a conventional printer system identifies an input color that may be classified as having a light tone 6. The system reproduces the light tone 6 as output color 16, including relatively few, isolated light tone pixels 10. Because of physical limitations of conventional printers, dies, and print media, some of the isolated light tone pixels identified as empty pixels 17, do not adhere to the print media and are wiped away or dispersed during the printing process.
The present invention addresses these and other problems.